This wouldn't happen in Illinois, because here, the change in signal phase begins when a signal switches from green to yellow, not later. We don't separate the yellow phase from the all-red phase and the next permissive phase of other traffic...it all happens together or not at all. If the signal commits to all 3 phases at once, the yellow trap is eradicated.

So basically, they aren't adaptive?

Adaptive, IDOT? Surely you must be joking. The most adaptiveness they have is either the camera detectors or the loop detectors (varies by district). Otherwise, Dallas phasing is not found in most of the state (District 4 uses the FYAs like that around Peoria). District 1 (Chicagoland) does not do Dallas phasing of any kind, anywhere. If the signal is green with a protected left, the opposing direction will not have a green or green arrow of any kind. All opposing traffic must stop and wait for the left turn to be permissive. D1 also strongly prefers leading left turns at all times.

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"If you think this has a happy ending, you haven't been paying attention." - Ramsay Bolton

What are the advantages of a doghouse layout? There are many, many areas of the country that have never used doghouse layouts. Many use the 5-section towers exclusively. Somehow they are getting on just fine (I'd guess).

The only advantage that I can think of, with a doghouse display, is that you could have two sets of solid yellow arrows:

From my perspective - and this is very personal opinion - doghouse relays some information about intersection mode of operation, namely that turn lane is controlled separately. Moreover, even doghouse facing the other way relays such information. Same reason why stop and yield signs have their distinctive shape, if you will. I am used to doghouse design, and find that useful. But - as someone else on this forum often mentions - personal opinion emphasized.

This wouldn't happen in Illinois, because here, the change in signal phase begins when a signal switches from green to yellow, not later. We don't separate the yellow phase from the all-red phase and the next permissive phase of other traffic...it all happens together or not at all. If the signal commits to all 3 phases at once, the yellow trap is eradicated.

So basically, they aren't adaptive?

Adaptive, IDOT? Surely you must be joking. The most adaptiveness they have is either the camera detectors or the loop detectors (varies by district). Otherwise, Dallas phasing is not found in most of the state (District 4 uses the FYAs like that around Peoria). District 1 (Chicagoland) does not do Dallas phasing of any kind, anywhere. If the signal is green with a protected left, the opposing direction will not have a green or green arrow of any kind. All opposing traffic must stop and wait for the left turn to be permissive. D1 also strongly prefers leading left turns at all times.

Most, if not all intersections outside of downtown (timed) areas have loop or camera detectors around here. In theory, it's nice, because the signal adapt to what they see. But sometimes they go a little wonky, as I described earlier.

What are you getting at with Dallas phasing? I'm not sure what that has to do with anything.

What are the advantages of a doghouse layout? There are many, many areas of the country that have never used doghouse layouts. Many use the 5-section towers exclusively. Somehow they are getting on just fine (I'd guess).

From my perspective - and this is very personal opinion - doghouse relays some information about intersection mode of operation, namely that turn lane is controlled separately. Moreover, even doghouse facing the other way relays such information.

Seeing a doghouse or tower intersection from a way's away certainly relays to drivers that their left turn at that intersection is likely to be permissive (I've seen split phasing with 5-section signals). But I'm not sure how that would be advantageous to the driver. I understand that you are used to the doghouse. I am also very used to the doghouse (although 4- and 5-section PPLT displays are far from uncommon here), but short of being able to tell whether or not my left turn will be made permissively (from a distance), I've never found doghouses to be particularly helpful. I generally don't consider my "possible actions" at the next intersection until I'm actually there.

What are the advantages of a doghouse layout? There are many, many areas of the country that have never used doghouse layouts. Many use the 5-section towers exclusively. Somehow they are getting on just fine (I'd guess).

From my perspective - and this is very personal opinion - doghouse relays some information about intersection mode of operation, namely that turn lane is controlled separately. Moreover, even doghouse facing the other way relays such information.

Seeing a doghouse or tower intersection from a way's away certainly relays to drivers that their left turn at that intersection is likely to be permissive (I've seen split phasing with 5-section signals). But I'm not sure how that would be advantageous to the driver. I understand that you are used to the doghouse. I am also very used to the doghouse (although 4- and 5-section PPLT displays are far from uncommon here), but short of being able to tell whether or not my left turn will be made permissively (from a distance), I've never found doghouses to be particularly helpful. I generally don't consider my "possible actions" at the next intersection until I'm actually there.

Well.. Maybe somewhat irrelevant example since FYA is was not involved (although would be a good spot, IMHO) was on one of local intersections, where doghouse was replaced with 4-section with green arrow - which came up in the end of the cycle. There are 2 lanes (straight through and dedicated left turn) - there were 2 towers, 3 and 4 (+green arrow)); 1 tower per lane. Those replaces ol'good doghouse for left turn. Now what you do when you see a traffic light installed to match your lane turning green?.... TO my defense, I saw quite a few other people getting caught with same mistake on that spot. Didn't see any crashes, though - but light was reprogrammed to move protected turn to the beginning of the green phase. Something that wouldn't happen with a doghouse.Just to illustrate how doghouse can help by just being there.

Seeing a doghouse or tower intersection from a way's away certainly relays to drivers that their left turn at that intersection is likely to be permissive (I've seen split phasing with 5-section signals). But I'm not sure how that would be advantageous to the driver. I understand that you are used to the doghouse. I am also very used to the doghouse (although 4- and 5-section PPLT displays are far from uncommon here), but short of being able to tell whether or not my left turn will be made permissively (from a distance), I've never found doghouses to be particularly helpful. I generally don't consider my "possible actions" at the next intersection until I'm actually there.

With a FYA there are more opportunities for permissive left turns than there were with the old system. When traffic on the opposite side has both a green for straight and a green arrow for left turn my side can now have a flashing yellow for permissive left. With the doghouse red light that wasn't an option and traffic couldn't turn left during that phase, even if there was no opposing through traffic present. With the FYA that needless wait is now avoided.

The scenario you are describing is when the FYA is on while the adjacent through is still red. This is an aggressive setup that attempts to squeeze out every last ounce of capacity. But it adds very little increased capacity for leading left setups and creates a perceived yellow trap in lagging left setups (and perception is reality.. if a driver believes their left turn phase is ending it’s just as dangerous as an actual yellow trap). It’s confusing to see the left turn arrow flashing yellow when the adjacent through is still red and many agencies refuse to operate the FYA in this manner. In addition, many agencies favor leading left operation to prevent the perceived yellow trap situation altogether. If they do run lagging lefts, they tie the left turns together to ensure that they start and end simultaneously.

One other point. There is a scenario where a FYA will still lead to a yellow trap. It occurs when you have a lagging left FYA with a left turn case sign in the opposing direction. If there is a FYA/left turn case sign combination, then the FYA must be leading or a yellow trap will be introduced.

Seeing a doghouse or tower intersection from a way's away certainly relays to drivers that their left turn at that intersection is likely to be permissive (I've seen split phasing with 5-section signals). But I'm not sure how that would be advantageous to the driver. I understand that you are used to the doghouse. I am also very used to the doghouse (although 4- and 5-section PPLT displays are far from uncommon here), but short of being able to tell whether or not my left turn will be made permissively (from a distance), I've never found doghouses to be particularly helpful. I generally don't consider my "possible actions" at the next intersection until I'm actually there.

Seeing a doghouse or tower intersection from a way's away certainly relays to drivers that their left turn at that intersection is likely to be permissive (I've seen split phasing with 5-section signals). But I'm not sure how that would be advantageous to the driver. I understand that you are used to the doghouse. I am also very used to the doghouse (although 4- and 5-section PPLT displays are far from uncommon here), but short of being able to tell whether or not my left turn will be made permissively (from a distance), I've never found doghouses to be particularly helpful. I generally don't consider my "possible actions" at the next intersection until I'm actually there.

Seeing a doghouse or tower intersection from a way's away certainly relays to drivers that their left turn at that intersection is likely to be permissive (I've seen split phasing with 5-section signals). But I'm not sure how that would be advantageous to the driver. I understand that you are used to the doghouse. I am also very used to the doghouse (although 4- and 5-section PPLT displays are far from uncommon here), but short of being able to tell whether or not my left turn will be made permissively (from a distance), I've never found doghouses to be particularly helpful. I generally don't consider my "possible actions" at the next intersection until I'm actually there.

With a FYA there are more opportunities for permissive left turns than there were with the old system. When traffic on the opposite side has both a green for straight and a green arrow for left turn my side can now have a flashing yellow for permissive left. With the doghouse red light that wasn't an option and traffic couldn't turn left during that phase, even if there was no opposing through traffic present. With the FYA that needless wait is now avoided.

The scenario you are describing is when the FYA is on while the adjacent through is still red. This is an aggressive setup that attempts to squeeze out every last ounce of capacity. But it adds very little increased capacity for leading left setups and creates a perceived yellow trap in lagging left setups (and perception is reality.. if a driver believes their left turn phase is ending it’s just as dangerous as an actual yellow trap). It’s confusing to see the left turn arrow flashing yellow when the adjacent through is still red and many agencies refuse to operate the FYA in this manner. In addition, many agencies favor leading left operation to prevent the perceived yellow trap situation altogether. If they do run lagging lefts, they tie the left turns together to ensure that they start and end simultaneously.

One other point. There is a scenario where a FYA will still lead to a yellow trap. It occurs when you have a lagging left FYA with a left turn case sign in the opposing direction. If there is a FYA/left turn case sign combination, then the FYA must be leading or a yellow trap will be introduced.

The correct programming of a lagging left is to go straight from FYA to a green arrow. If the FYA is going to solid yellow and red before going to the solid green, the signal is programmed wrong. If the signal is programmed correctly, the perceived yellow trap should not occur.

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From my perspective - and this is very personal opinion - doghouse relays some information about intersection mode of operation, namely that turn lane is controlled separately. Moreover, even doghouse facing the other way relays such information. Same reason why stop and yield signs have their distinctive shape, if you will. I am used to doghouse design, and find that useful. But - as someone else on this forum often mentions - personal opinion emphasized.

One of the big reasons I'm a huge fan of the FYA is it encourages 1 signal per lane. I'm a firm believer that the "best" (obviously my personal opinion) method is to allow signals to very clearly indicate the permitted directions of the lane, as the markings painted on the road are often covered by other cars and are often faded without being fixed for extremely long times. I'd like to see the FYA replace the right turn doghouses as well. Doghouses should be relegated to shared use lanes. Then nearly every lane configuration will be clear on green by what its signal has displayed. And for the most part, it will be fairly obvious on red with the same information (just not illuminated multiple movements per lane).

This is an aggressive setup that attempts to squeeze out every last ounce of capacity. But it adds very little increased capacity for leading left setups and creates a perceived yellow trap in lagging left setups (and perception is reality.. if a driver believes their left turn phase is ending it’s just as dangerous as an actual yellow trap). It’s confusing to see the left turn arrow flashing yellow when the adjacent through is still red and many agencies refuse to operate the FYA in this manner. In addition, many agencies favor leading left operation to prevent the perceived yellow trap situation altogether. If they do run lagging lefts, they tie the left turns together to ensure that they start and end simultaneously.

Total bollocks. There are FYAs in nearly all jurisdictions within 400 miles of me , yet not a single one (AFAIK) operates FYAs in this manner, probably because it doesn't make any sense. Some do have odd quirks:

- protected-only based on time of day (although increasingly normal)- longer all-red phases between the protected and permissive phase (though some have none, such as many left turns in Seattle)- red while pedestrian has walk sign

...but none have any sort of through/left synchronization. That completely ruins the whole point of the FYA. I understand the perception, but I think in reality, this has more to do with poor signal placement, where drivers can only see the left turn signal in their upper peripheral vision. Federal Way, WA (an agency near me that I have brought up just about a thousand times before) uses lead/lag or lagging at almost every intersection. They also go protected-only during parts of the day. Needless to say, they are using the FYA to the fullest extent possible. Yet not a single shred of data that I've ever read, in regards to FYA performance in the city, suggests in increase due to perceived yellow trap. There's not a lot of publicly available data, but one the PDFs from several years ago suggests that FYAs seem to work better when there's secondary/auxiliary signals (PDF page 14). Also, that safety performance improves dramatically after the first year.

I was somewhat skeptical of the benefits of the FYA. Then we had several installed nearby. I now get it and would never go back to the old way. Local drivers adapted very quickly to the new system.

With a FYA there are more opportunities for permissive left turns than there were with the old system. When traffic on the opposite side has both a green for straight and a green arrow for left turn my side can now have a flashing yellow for permissive left. With the doghouse red light that wasn't an option and traffic couldn't turn left during that phase, even if there was no opposing through traffic present. With the FYA that needless wait is now avoided.

This is the main reason why I would like the FYA to be introduced in Ontario. We don't need it to solve yellow traps, since Ontario only allows lagging lefts if there's no opposing left turn. But it would be nice to be able to make a left turn in the situation you describe.

The correct programming of a lagging left is to go straight from FYA to a green arrow. If the FYA is going to solid yellow and red before going to the solid green, the signal is programmed wrong. If the signal is programmed correctly, the perceived yellow trap should not occur.

An example of a perceived yellow trap can be seen at 0:39 in this video. Drivers in the left turn lane who see the adjacent signal heads change to yellow automatically assume the opposing through direction is changing to yellow at the same time. Before the FYA came into existence, this assumption was almost always correct (because if the opposing thru wasn't changing to yellow simultaneously, it would lead to a yellow trap) . But now drivers have to realize that the opposing thru may still have a green light when the adjacent thru changes to yellow.

I was somewhat skeptical of the benefits of the FYA. Then we had several installed nearby. I now get it and would never go back to the old way. Local drivers adapted very quickly to the new system.

With a FYA there are more opportunities for permissive left turns than there were with the old system. When traffic on the opposite side has both a green for straight and a green arrow for left turn my side can now have a flashing yellow for permissive left. With the doghouse red light that wasn't an option and traffic couldn't turn left during that phase, even if there was no opposing through traffic present. With the FYA that needless wait is now avoided.

So basically, FYA makes Left on Red legal?

Why not just make Left on Red legal then? Why do we need new stoplights?

If there is no opposing traffic, why wait at a stoplight, going Straight or Left?

I was somewhat skeptical of the benefits of the FYA. Then we had several installed nearby. I now get it and would never go back to the old way. Local drivers adapted very quickly to the new system.

With a FYA there are more opportunities for permissive left turns than there were with the old system. When traffic on the opposite side has both a green for straight and a green arrow for left turn my side can now have a flashing yellow for permissive left. With the doghouse red light that wasn't an option and traffic couldn't turn left during that phase, even if there was no opposing through traffic present. With the FYA that needless wait is now avoided.

So basically, FYA makes Left on Red legal?

Why not just make Left on Red legal then? Why do we need new stoplights?

There's a big difference between making a left when oncoming traffic has a green+arrow vs the side street having a green...

I was somewhat skeptical of the benefits of the FYA. Then we had several installed nearby. I now get it and would never go back to the old way. Local drivers adapted very quickly to the new system.

With a FYA there are more opportunities for permissive left turns than there were with the old system. When traffic on the opposite side has both a green for straight and a green arrow for left turn my side can now have a flashing yellow for permissive left. With the doghouse red light that wasn't an option and traffic couldn't turn left during that phase, even if there was no opposing through traffic present. With the FYA that needless wait is now avoided.

So basically, FYA makes Left on Red legal?

Why not just make Left on Red legal then? Why do we need new stoplights?

There's a big difference between making a left when oncoming traffic has a green+arrow vs the side street having a green...

Not really -- depends how much oncoming traffic is coming, and how much cross traffic there is, while your light is red. It might actually be safer, depending on the street, with the cross street having the green, for the Left on Red

But the justification is, if there is no opposing traffic

If there is no opposing traffic, whether oncoming or cross, why stop anyway? Isn't that the point of stoplights?

The correct programming of a lagging left is to go straight from FYA to a green arrow. If the FYA is going to solid yellow and red before going to the solid green, the signal is programmed wrong. If the signal is programmed correctly, the perceived yellow trap should not occur.

An example of a perceived yellow trap can be seen at 0:39 in this video. Drivers in the left turn lane who see the adjacent signal heads change to yellow automatically assume the opposing through direction is changing to yellow at the same time. Before the FYA came into existence, this assumption was almost always correct (because if the opposing thru wasn't changing to yellow simultaneously, it would lead to a yellow trap) . But now drivers have to realize that the opposing thru may still have a green light when the adjacent thru changes to yellow.

^^Trade, unless you intend to provide some hard evidence that this perceived yellow trap is an actual issue, your point is moot.

The TRB contains literature that discusses the "perceived" yellow trap at FYA:

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Methods for Operation and Detection of the Flashing Yellow Arrow Display: The Flashing Yellow Arrow (FYA) display is a form of protected-permitted left-turn phasing (PPLT) approved in 2006 by the National Committee on Uniform Traffic Control Devices and is anticipated for inclusion in the next release of the MUTCD. The FYA display eliminates the yellow trap, allows lead-lag phasing with PPLT, and allows time of day selection of protected-only or permitted-only phasing. This paper describes operational and efficiency benefits of the Flashing Yellow Arrow display and how they are achieved by selection of phasing, timing elements, and modified detection methods. In addition, the paper will describe some lessons learned that will be valuable for other engineers who are contemplating or just starting to use the FYA. The question then becomes how the traffic engineer should utilize the power and flexibility of the FYA display and when to exercise restraint. The real power of the FYA becomes available when the engineer starts to break away from “leading lefts only” phasing typically required by traditional PPLT. This paper will discuss different phasing options with the FYA and the pluses and minuses of each in terms of what existing problems they might solve or mitigate. Along with this will be a discussion of detection strategies from simple to complex that can greatly improve the efficiency of the FYA. Finally, there will be a description of a “perceived” yellow trap that can occur in some circumstances with the FYA and how to recognize when it may be a problem.

Beyond that there are agencies that prefer leading lefts over lagging lefts at FYA. They cite the "perceived yellow trap" issue in their reasoning. Here’s a snippet from a webinar by the Oregon Transportation Research and Education Consortium about whether or not the FYA solves the yellow trap:

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Q: What degree does the FYA solve the “yellow trap” problem. And does Washington County lead the protected interval at FYA or lead/lag to benefit coordination?

A: The FYA completely solves the yellow trap problem, because now the left turn lane has its own display. There is still the potential of the “perceived yellow trap” which is when the driver in the left lane sees the adjacent through go solid yellow and thinks that the FYA is also ending. It is called perceived, because the driver should focus on their own lane’s signal control. Washington County prefers to lead the protected interval at FYA so if the protected left isn’t needed then it can be skipped. In a coordinated system we will lead or lag whichever benefits the coordination. (SS)

You can still skip a protected left turn at a lagging FYA but it sounds like Washington County chooses not to do that. They don't want to introduce the perceived yellow trap, so presumably they tie the lagging left turns together to run simultaneously. Jake, don't you live near Washington County, Oregon? You tell me how the lagging left installations run there and if any perceived yellow traps exist.

You can still skip a protected left turn at a lagging FYA but it sounds like Washington County chooses not to do that. They don't want to introduce the perceived yellow trap, so presumably they tie the lagging left turns together to run simultaneously. Jake, don't you live near Washington County, Oregon? You tell me how the lagging left installations run there and if any perceived yellow traps exist.

I have seen lead/lag in the Portland area but I cannot remember where. I've only been there twice in the last five years. I'd be more likely to remember if lead/lag were uncommon where I live, but it's not. But, I would remember an installation that has an FYA that's tied to the through lane (an installation where the permissive phase starts only with the through lane). That I am certain I have not seen.

The correct programming of a lagging left is to go straight from FYA to a green arrow. If the FYA is going to solid yellow and red before going to the solid green, the signal is programmed wrong. If the signal is programmed correctly, the perceived yellow trap should not occur.

An example of a perceived yellow trap can be seen at 0:39 in this video. Drivers in the left turn lane who see the adjacent signal heads change to yellow automatically assume the opposing through direction is changing to yellow at the same time. Before the FYA came into existence, this assumption was almost always correct (because if the opposing thru wasn't changing to yellow simultaneously, it would lead to a yellow trap) . But now drivers have to realize that the opposing thru may still have a green light when the adjacent thru changes to yellow.

I guess I understand what you're saying, but the entire point of the FYA is so it is the only signal you look at for making your left turn. Again, that is why I really want to see a total movement to a signal per lane system to further reinforce that point. The only reason people are looking at the thru signals is because they're used to the previous permissive setup with a green ball without a red arrow indicating the permissive turn. It would seem that new drivers who don't encounter the old permissive signals would not be used to looking at the thru signal to determine if they can turn, so its a driver experience/dealing with change problem that should fade with time. And regardless, the same signal setup without the FYA would result in an actual yellow trap, which is far worse then a possible perceived one. The fact the left turn signal hasn't changed should make them at least hesitate about going on the thru yellow, which is why I think this isn't really a real problem.

I was somewhat skeptical of the benefits of the FYA. Then we had several installed nearby. I now get it and would never go back to the old way. Local drivers adapted very quickly to the new system.

With a FYA there are more opportunities for permissive left turns than there were with the old system. When traffic on the opposite side has both a green for straight and a green arrow for left turn my side can now have a flashing yellow for permissive left. With the doghouse red light that wasn't an option and traffic couldn't turn left during that phase, even if there was no opposing through traffic present. With the FYA that needless wait is now avoided.

So basically, FYA makes Left on Red legal?

Why not just make Left on Red legal then? Why do we need new stoplights?

There's a big difference between making a left when oncoming traffic has a green+arrow vs the side street having a green...

Not really -- depends how much oncoming traffic is coming, and how much cross traffic there is, while your light is red. It might actually be safer, depending on the street, with the cross street having the green, for the Left on Red

But the justification is, if there is no opposing traffic

If there is no opposing traffic, whether oncoming or cross, why stop anyway? Isn't that the point of stoplights?

In the scenario that cjw2001 outlined, to make the permissive left, you only have to yield to cars going straight or right from the opposing direction and pedestrians on the left. This is the same as a regular permissive left at a green light, so I have a hard time seeing how this is anymore dangerous than that (assuming there's an FYA, so people know what you're doing).

But doing a left from a red light when cross traffic has the green has many more potential conflicts and it confuses the drivers around you. Theoretically, if no one's around, then it's safe, but it's better to keep it illegal at all times since it's generally a more dangerous manoeuvre than a permissive left turn.

Maybe its just my learned driving habits, but a Permissive Left Turn phase should coincide with your "Thru" traffic having a Green Signal for the straight movement

There is no way it is safer for Left Turners than it is for Straight/Through traffic in this situation (if the Opposing direction has Protected Green Left Turn combined with Green for Straight/Through traffic.) At worst, it should be "Flashing Yellow" for Left Turning AND Straight/Through Traffic

It is pretty easy to dream up a scenario where Oncoming/Opposing Traffic has a Green Ball with Green Left Arrow, and there is traffic going straight but not turning. Why shouldn't the "Other" direction's straight movement have a "Permissive" Straight movement with a Flashing Yellow Ball, if Left Turning movement can have a "Permissive" Left movement with a Flashing Yellow Arrow

Maybe its just my learned driving habits, but a Permissive Left Turn phase should coincide with your "Thru" traffic having a Green Signal for the straight movement

There is no way it is safer for Left Turners than it is for Straight/Through traffic in this situation (if the Opposing direction has Protected Green Left Turn combined with Green for Straight/Through traffic.) At worst, it should be "Flashing Yellow" for Left Turning AND Straight/Through Traffic

It is pretty easy to dream up a scenario where Oncoming/Opposing Traffic has a Green Ball with Green Left Arrow, and there is traffic going straight but not turning. Why shouldn't the "Other" direction's straight movement have a "Permissive" Straight movement with a Flashing Yellow Ball, if Left Turning movement can have a "Permissive" Left movement with a Flashing Yellow Arrow

I'm looking for consistency here

Its important to remember that any flashing yellow signal ultimately means proceed using the rules of the road as if there was no signal here (but with caution). A yellow flashing ball would seem to have priority for those approaching it over the green arrow (that they can't see), as its not the normal rule of the road.

Another benefit of having the FYA display alongside a red ball is it introduces familiarity of this necessary situation to avoid yellow trap in some scenarios. And getting drivers familiar with that display seems it would reduce the risk of a "perceived yellow trap"